With the recent development of mobile communication and information electronic devices, demand for high-capacity and light-weight lithium ion secondary batteries tends to be increased. Most of electrolytes that exhibit high lithium ion conductivity at room temperature are liquids, and many of commercially-available lithium ion secondary batteries use an organic electrolyte solution. Lithium ion secondary batteries that use this organic electrolyte solution involves a risk of leakage, ignition and explosion, and hence a safer battery has been demanded.
An all-solid battery using a solid electrolyte obtained by mixing a lithium compound, a halogen compound, and phosphorus sulfide in place of the organic electrolytic solution has a feature that leakage and ignition of the electrolyte hardly occur. Here, as the solid electrolyte, a sulfide-based solid electrolyte having high safety and high ionic conductivity has been developed (Patent Documents 1 to 3).
The sulfide-based solid electrolytes disclosed in Patent Documents 1 to 3 exhibit high ionic conductivity by crystallizing sulfide glass by subjecting it to a heat treatment. However, a heat-treatment temperature range at which a high ionic conductivity is exhibited is narrow, and hence production is difficult. In particular, there is a problem that if large-sized production equipment is used in order to conduct mass production, heating at uniform temperatures becomes difficult.